Psoriasis is a chronic inflammatory skin disease that manifests as erythematous, dry, scaling plaques resulting from hyperkeratosis. The plaques are most often found on the elbows, knees and scalp, though more extensive lesions may appear on other parts of the body, notably the lumbosacral region. The most common treatment of mild to moderate psoriasis involves topical application of a composition containing a corticosteroid as the active ingredient. While efficacious, application of corticosteroids has the disadvantage of a number of adverse effects such as skin atrophy, striae, acneiform eruptions, perioral dermatitis, overgrowth of skin fungus and bacteria, hypopigmentation of pigmented skin and rosacea.
For many years, however, an advantageous non-steroidal treatment of psoriasis has consisted in topical treatment with the vitamin D analogue compound, calcipotriol, formulated in an ointment composition (marketed as Daivonex® or Dovonex® ointment by LEO Pharma) in which the calcipotriol is present in solution or a cream composition (marketed as Daivonex® or Dovonex® cream by LEO Pharma). The solvent in the ointment composition is propylene glycol which has the advantage of enhancing penetration of the active Ingredient into the skin, leading to an improved efficacy, but which is also known to act as a skin Irritant. Thus, it has been reported that the inclusion of propylene glycol in topical compositions frequently causes patients to develop contact dermatitis (one study reported a number of irritant reactions to propylene glycol of 12.5%, cf. M. Hannuksela et al., Contact Dermatitis 1, 1975, pp. 112-116), and the number of irritant reactions increases when propylene glycol is used in high concentrations (as reviewed by J. Catanzaro and J. Graham Smith, J. Am. Acad. Dermatol. 24, 1991, pp. 90-95). Due to the improved penetration of calcipotriol into the skin resulting, inter alia, from the presence of propylene glycol, Daivonex® ointment has been found to be more efficacious in the treatment of psoriatic lesions than Dalvonex®  cream, but has also caused skin irritation in a significant proportion of psoriasis patients.
More recently, a combination product for the treatment of psoriasis has been marketed by LEO Pharma under the trade name Daivobet® ointment. The product comprises calcipotriol and betamethasone dipropionate as the active ingredients formulated in an ointment composition in which calcipotriol is dissolved in polyoxypropylene-15-stearyl ether and betamethasone dipropionate is present as a suspension. While the efficacy of the combination is significantly superior to that of either active ingredient on its own, the ointment may be perceived as cumbersome to apply as it requires prolonged rubbing into the skin of the affected area, and many patients, in particular those with extensive psorlatic lesions would favour a greater ease of application such as is provided by a spray composition. Daivobet® ointment does not contain any penetration enhancer such as propylene glycol which has been found to be detrimental to the chemical stability of calcipotriol (cf. example 2 of WO 00/64450). It is considered desirable to further improve the biological efficacy of the combination of the two active ingredients by providing a formulation vehicle from which penetration of the active ingredients into the skin is improved compared to the commercial product.
WO 00/64450 dicloses a pharmaceutical composition comprising a vitamin D analogue and a corticosteroid formulated in a solvent containing vehicle in which both active ingredients are chemically stable. The preferred embodiment of the composition is an ointment and there is no mention of providing a spray composition with improved properties compared to an ointment.
US 2005/0281749 discloses a spray composition comprising a corticosteroid and a vitamin D derivative solubilised in an oily phase composed of one or more oils. The oil may be selected from a vegetable, mineral, animal, synthetic or silicone oil. There is no suggestion that it might be desirable to provide occlusion and consequently it is not proposed to add a semi-solid and occlusive excipient to the composition. There is no indication whether the composition exhibits improved penetration properties.
US 2005/0281754 discloses a spray composition comprising a corticosteroid and a vitamin D derivative formulated in a vehicle comprising an alcohol phase and an oil phase. The alcohol phase is composed of for instance ethanol, isopropanol or butanol. The oil phase may be composed of a mineral, vegetable or synthetic oil. There is no suggestion of including a semi-solid and occlusive excipient to the composition, and no indication whether the composition exhibits improved penetration properties.